1. Field of the Invention
The present invention relates to methods for welding together corrugate membranes and, more particularly, to methods for welding corrugate portions by means of a welding robot for corrugation lap joint.
2. Description of Related Arts
In the welding of corrugate membranes, it has been a conventional practice to employ a contact-type sensor for shape recognition and a tracer control system for the control of the torch angle of a welding torch. Where a plasma arc welding process which is faster in the welding speed than a conventional TIG welding process is employed for the welding of membranes, the tracer control of the welding torch for the welding of corrugate portions is more liable to cause a welding failure because the torch angle control cannot follow up the sensing of the contact-type sensor. To this end, a delayed control system has been proposed in which a sensor travels ahead of a welding torch to allow the welding torch to follow up the sensor more easily. In the high-speed plasma arc welding process, the delayed control system allows the welding torch to appropriately trace a weld line by comparing a corrugate configuration of a membrane to be welded with preliminarily provided corrugation NC data and determining the corrugate configuration.
Where the welding speed and the torch angle with respect to the weld line are controlled to be constant by utilizing the corrugation NC data corresponding to the corrugate configuration, a welding failure tends to occur in the following portions:
(1) where the inclination drastically changes; PA1 (2) where residual heat of welding adversely affects a weld bead; and PA1 (3) where different welding conditions are required because the membrane is mounted in a different orientation.
In the welding of corrugate portions by a conventional welding robot, every membrane is considered to have the same corrugate configuration. Corrugation NC data to be utilized when a robot control software is implemented are selected based on the corrugate configuration, and the welding of the corrugate portions is controlled by the delayed control system. Where the membranes do not have exactly the same corrugate configuration or where the positioning of the membranes is inappropriate, however, the corrugate portions may be deformed when the membranes are temporarily welded. In such a case, when a welding torch traces a weld line based on the aforesaid standard corrugation NC data, the welding torch may miss a welding target due to the deformation of the corrugate portions, thereby causing a welding failure.